Automated root cause analaysis
Defect identified in software had been present since it was written in the 1990s
Another IT failure causes flight disruption as London airspace is closed due to an IT glitch
NATS says issue is "very complex and sophisticated with more than a million lines of software"
Operations now returning to normal, claims NATS
NATS admits computer problems at its Swanwick computer centre - but UK airspace not closed